This invention relates generally to microelectronic structures and devices and to a method for their fabrication, and more specifically to structures and devices including piezoelectric thin films and to the fabrication and use of the structures and devices.
Piezoelectric materials are useful for a variety of applications. For example, piezoelectric material is often used to form pressure gauges, transducers, tactile sensors, robotic manipulator, high frequency sound generators, frequency control circuits, and oscillators.
Generally, the desirable characteristic of the piezoelectric material, i.e., the piezoelectric effect, increases as the crystallinity of the material increases. Accordingly piezoelectric material of high crystalline quality if often desired.
Piezoelectric material is relatively expensive in bulk form compared to other materials used to form microelectronic devices such as microelectronic pressure sensors, oscillators, and the like. Because of their present generally high cost and low availability in bulk form, for many years attempts have been made to grow thin films of the piezoelectric materials on a foreign substrate. To achieve optimal characteristics of piezoelectric material, however, a monocrystalline film of high crystalline quality is desired. Attempts have been made, for example, to grow layers of a monocrystalline piezoelectric material on substrates such as silicon. These attempts have generally been unsuccessful because lattice mismatches between the host crystal and the grown crystal have caused the resulting thin film of piezoelectric material to be of low crystalline quality.
If a large area thin film of high quality monocrystalline piezoelectric material was available at low cost, a variety of semiconductor microelectronic devices could advantageously be fabricated using that film at a low cost compared to the cost of fabricating such devices on a bulk wafer of the piezoelectric material. In addition, if a thin film of high quality monocrystalline piezoelectric material could be realized on a bulk wafer such as a silicon wafer, an integrated device structure could be achieved that took advantage of the best properties of both the silicon and the piezoelectric material.
Accordingly, a need exists for a microelectronic structure that provides a high quality monocrystalline piezoelectric film over another monocrystalline. material and for a process for making such a structure.